The present invention relates to a light scanning device employed for an electrophotographic type image forming device.
There is widely known as a light scanning device employed for an electrophotographic type image forming device such as a laser printer, copy machine, and facsimile machine a light scanning device configured such that a laser beam emitted by a light source is deflected by a polygon mirror being rotated. To meet a requirement for faster processing of the image forming device, there is desired a faster rotational speed of a drive motor that drives the polygon mirror of the light scanning device. In addition, an optical box constituting the optical scanning device has a sealed structure to prevent vibrations and/or noises accompanying the faster rotational speed of the drive motor from leaking outside the optical box and prevent dust from coming into the optical box. Therefore, such a sealed structure causes a problem that heat generated due to the faster rotational speed of the drive motor is stored up inside the optical box and affects optical components in the optical box. A conventional typical optical scanning device is disclosed, for example, in Japanese Granted Patent Publication No. 3075497 (hereinafter, referred to as '497 Publication).
Configuration examples of the light scanning device described in '497 Publication are shown in FIGS. 9-11. FIG. 9 schematically shows a configuration of the light scanning device. FIG. 10 is a cross-sectional view of the light scanning device along an X-X line shown in FIG. 9. The light scanning device has an optical box 3 provided with a light source 4, motor 7, lens system 13, circuit board 6, and polygon mirror 19. The optical box 3 is configured to be sealed with a cover member 5, metal portion 9 with high thermal conductivity, resin portion 11 (shaded area in the figures) with low thermal conductivity, motor 7, and cover glass 3a. The motor 7 includes a motor attachment member 17, motor main body 15, rotation axis 18 passing through the motor main body 15, and motor bearing portion 16. The motor attachment member 17 is fixed to the metal portion 9 as well as the circuit board 6. The polygon mirror 19 is fixed to the rotation axis 18.
A laser beam emitted by the light source 4 is deflected by the polygon mirror 19 being rotated, and illuminates a photo conductor outside the optical box 3. The heat generated due to the motor 7 is transmitted through the metal portion 9, and radiated from the metal portion 9 and motor bearing portion 16 to the outside of the optical box 3.
In addition, FIG. 11 shows another example of the light scanning device described in '497 Publication. The same reference numbers as those in FIG. 10 are given to the same portions as those in FIG. 10. In an optical box 30 shown in FIG. 11, a metal portion 90 is formed integrally with a cover member 50. The motor 7 is configured to contact with a resin portion 110 (shaded area) with low thermal conductivity (a cover glass 30a has low conductivity as well). Accordingly, the heat generated due to the motor 7 inside the optical box 30 is radiated outside the optical box 30 via the metal portion 90 with the high conductivity.
However, according to the light scanning device disclosed in '497 Publication, since the heat generated due to the motor 7 is radiated outside the optical box 3, the optical box 3 is required to be manufactured with the metal portion 9 being formed integrally with resin portion 11. It leads to a higher manufacture cost. In addition, the motor bearing portion 16 exposed outside the optical box 3 might be contaminated with dust. Further, in the optical box 3, the motor 7 and lens system 13 are provided on different bases, respectively (that is, the motor 7 is provided on the metal portion 9, while the lens system 13 is provided on the resin portion 11). Therefore, when a relative position of the metal portion 9 with respect to the resin portion 11 is even slightly displaced, it might cause a problem that the laser beam deflected by the polygon mirror 19 does not conform to the optical axis of the lens system 13. It is noted that the optical box 30, in which the motor 7 and lens system 13 are provided on the resin portion 110, has lower heat radiation efficiency than the optical box 3, as the metal portion 90 having a function of radiating the heat is interspatially located away from the motor 7.